Some parents are now questioning that policy. 9NEWS received two news tips in two weeks from different parents concerned about their children being inadvertently exposed to pornography.

Library officials insist they are only following the law.

In the adult section of Jeffco libraries, it's OK to watch porn on computers as long as you use a privacy screen. 9NEWS spoke with a parent who says she and her 5-year-old son saw much more than they should have seen in a public place.

Berry says a teenager was viewing an X-rated movie on a Columbine Library computer, and appeared to be touching himself underneath his clothing.

"The patron was lying back in his chair, he had his hand down his pants, and was clearly masturbating," Berry said.

Berry complained to the librarian and expected the teen to be thrown out. But 20 minutes later, she says he was still in the library.

"He was on the exact same computer," Berry said. "He hadn't been kicked out of the library. He hadn't been kicked off the computers. He was still sitting there."

Berry called the Jefferson County Sheriff's Office. The 17-year-old got a ticket for trespassing and could face charges of indecent exposure. A sheriff's spokesperson confirmed deputies have responded to other incidents involving people watching porn at Jeffco libraries.

"My first reaction is that we're very sorry if a child in the library was exposed to material that they found objectionable," said Rebecca Winning, associate director of communications and public engagement for the Jefferson County Public Library.

Winning says the library tries to protect kids by keeping the children's section separate from the adult section.

"So kids could come to the library, go to the children's area and get all their needs met, and never even walk by [the adult area]," Winning said.

Winning says the Jeffco library board has decided that a public library cannot control what adults watch.

"We follow the law," Winning said. "If the law allows access to certain information that you or I might find objectionable, we allow patrons to access it."

The policy on pornography varies with each library system. In April, library officials in New York City said pornography is protected by the First Amendment. Other local libraries, including Denver and Aurora, don't allow porn. In Denver, anyone caught watching it is told to leave and could be banned for repeat offenses.

Jeffco library computers used by children are equipped with anti-pornography filters, as required by the government. Unfiltered computers are available for adults. Any legal content, including hardcore porn, is allowed.

"We do ask patrons to use a privacy screen," Winning said, adding the library has only gotten a handful of complaints about people viewing pornography.

"We serve the entire population," Winning said, "the entire spectrum, from children to adults."

Berry wants Jeffco to change its policy, so nobody else gets an unwanted lesson at the library.

"I think the library should block those sites," Berry said. "I mean, [somebody] needs to say this is not acceptable behavior in a public place."